Method of improving the grindability of alumina-silica ores

ABSTRACT

A method of improving the grindability or grinding characteristics of aluminus clays or alumina-silica ores containing iron species by thermally treating the clays or ores at relatively high temperature in an air or oxidative atmosphere and subsequently grinding ore to a predetermined particle size, whereby the amount of fines produced on grinding are substantially less than the amount of fines produced upon grinding a comparable non-calcined ore.

United States Patent 1 1 1111 3,730,445

Lee et al. May 1, 1973 54] METHOD OF IMPROVING THE 2,368,194 1/1945 Brenner ..241/23 x GRIND ABILITY 0F ALUMINASILICA 2,899,278 8/1959 Lewis ..241/23 ORES Inventors: Thomas E. Lee; Frederick W. Frey, both of Baton Rouge, La.

Related US. Application Data Division of Ser. No. 74,169, Sept. 2, 1970.

[52] U.S. Cl ..241/23, 241 25 [51] Int. Cl ..B02c 23/00 [58] Field of Search ..241/23, 25, 18

[56] References Cited UNITED STATES PATENTS 2,304,440 12 1942 Brenner et al ..241/23 Primary ExaminerGranville Y. Custer, Jr. Att0rneyDonald L. Johnson et a1.

[5 7] ABSTRACT A method of improving the grindability or grinding characteristics of aluminus clays or alumina-silica ores containing iron species by thermally treating the clays or ores at relatively high temperature in an air or oxidative atmosphere and subsequently grinding ore to a predetermined particle size, whereby the amount of fines produced on grinding are substantially less than the amount of fines produced upon grinding a comparable non-calcined ore.

10 Claims, No Drawings METHOD OF IMPROVING THE GRINDAIBILITY F ALUMINA-SILICA ORES This is a division, of application Ser. No. 74,169, filed on Sept. 20, 1970.

BACKGROUND OF THE INVENTION The present invention is in the broad field of metallurgy and relates primarily to the beneficiation of aluminus clays or alumina-silica ores for subsequent use in the production of aluminum-silicon alloys.

Natural clays or ores containing aluminum-silicates or alumina-silica usually contain relatively large amounts of iron species generally in the forms of ferrous and/or ferric oxide. Such iron is a harmful impurity in the production of aluminum-silicon alloys. Unless the iron species are removed from the ore prior to car bothermic reduction for producing aluminum-silicon alloys, the resulting aluminum-silicon alloy end product will contain undesirable amounts of iron. In general,- the freer an aluminum-silicon alloy is of other elements, the more useful is the alloy. Alloys containing low amounts of iron are therefore extremely desirable.

The present process is primarily adapted for removing or lowering the iron species content of alumina-silica ores prior to their carbothermic reduction into aluminum-silicon alloys. It has been discovered that calcining or thermal treatment of the raw ore or aluminum clay in an air or oxidative atmosphere promotes the agglomeration of the iron containing species and their more facile separation from the aluminus material by magnetic methods. An additional benefit of the calcination or roasting is that the grinding characteristics of the ore are modified so that less fines are produced on grinding thereby resulting in a lower loss of valuable material.

It is therefore a primary object of the present invention to provide an economical method of physically beneficiating alumina-silica ores for use in the production of aluminum-silicon alloys.

SUMMARY OF THE INVENTION Natural alumina-silica clays or clay minerals are heated in an oxidative atmosphere to a temperature of from about ll00 C to about l400 C for a period of about 2 hours to about 48 hours. The calcined ore is then ground and/or crushed into fine particles of a mesh size from about 40 to +400 U. S. Sieve Series. The magnetic iron values are then separated from the non-magnetic mineral values by magnetic separation.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the preferred embodiment of the invention a natural alumina-silica clay or clay mineral such as diaspore clay previously crushed or ground to a convenient size usually about 3 mesh, U. S. Sieve Series is heated in a kiln or other suitable container to a temperature of about l300-l400 C in air, oxygen or other suitable oxidative atmosphere for a period of from about 2-5 hours.

Prior to calcining, the ore particles should be of a size to permit convenient handling thereof. Although the particle size of the raw ore is not critical, an initial particle size of about one-quarter inch to about onehalf inch in diameter produces favorable results. After calcining or oxidative roasting, the ore is ground to a fine particle size of about -40 on 400 mesh, -U. S." Sieve Series.

The particles of ore are then magnetically separated by any suitable means. An induced roll high intensity magnetic separator has been found to be satisfactory. Calcination in air or an oxidative atmosphere agglomerates the iron species and improves their magnetic properties enabling the iron species to be more readily removed by magnetic separation. An air flush preheated to about 1000 C and introduced during calcination of the clay or ore at a rate of about 2-3 cubic feet per minute produces exemplary results.

Preheating of the air or oxidation medium permits conservation of heat energy and makes the process more economical. The quantity of air, oxygen or other suitable oxidation medium should be sufficient to 'accomplish the desired oxidation or agglomeration. The rate the air or oxidation medium is introduced during calcining will vary with the size and type of equipment used in the process.

Although the present invention is suitable for beneficiation of any alumina-silica ores, it is especially useful in the beneficiation of diaspore clay and kyanite clay, or clays containing diaspore, boehmite and/or kaolinite and iron species. Although not wishing to be bound by any particular theory, it is believed that the following occurs during Calcination:

The following examples are illustrative of the invention:

EXAMPLE A A composite sample of diaspore clay containing diaspore, boehmite and kaolinite as predominant minerals and small amounts of siderite, goethite and hematite of about 4/40 mesh was heated in air for two hours in a furnace at a temperature of l380-l4l0 C. The resulting material had visible spots and nodules of magnetic iron oxide. The sample was crushed in a mortar and pestle to percent minus 40 mesh. Approximately 17 percent was separated with a small hand magnet. The magnetic fraction was black and shiny in appearance. The non-magnetic fraction still had black particles in it. Conversely, no magnetic fraction could be separated from an original non-calcined diaspore clay sample with the same small hand magnet.

EXAMPLE B EXAMPLE C Two diaspore clay samples, containing diaspore,

boehmite and kaolinite as predominant minerals and small amounts of siderite, goethite and hematite, of 550 grams each were calcined in air at 1300 C i C in a furnace for approximately six hours. The two batches were ground together for 15 minutes in a 9-inch laboratory rod mill. A wet sieve analysis of the ground mixure. is shown. i a leji g s nafts s TABLE 1 Wet Sieve Analysis Mesh Wt Wt +30 173.8 22.3 30/40 123.0 15.8 40/100 313.0 40.2 100/200 103.6 13.3 200/270 33.1 4.2 270/400 30.6 3.9 400 N. A. N. A.

EXAMPLE E Two diaspore clay samples, containing diaspore, .boehmite, and kaolinite as predominant minerals and small amounts of siderite, goethite and hematite, of 670 grams each and of a particle size of 3/40 mesh were tested for their grindability or grinding characteristics. One sample was calcined at 1300 C for approximately 6 hours. Each of the samples was then separately ground dry in a laboratory rod mill for 15 minutes. Subsequently the particle size of the samples and the amount of each particle were determined. The calcined sample produced about 25 percent fewer fines (-400 mesh) than the non-calcined sample. The results of these tests are set forth in Table IV hereinafter.

TABLE IV Sample Original (Non-calcined Calcined 17.4 68.7 13.6

TABLE II.-1\IAGNETIC sEPARAglAoblgsoF DIASPORE-CLAYAT 11,000

Weight percent Fraction of total 77F Percent Percent Mesh Sample No. A110; 810; P0 03 T101 \\'t. FeZOa 1103 size 1 {Magnetic 50.9 35. 8 10.0 3.3 128.0 70.11 38.1 40/100 Non-magnetic... 54. 2 39. 8 2. 7 3.3 183.9 29.1 61.7 2 {)lagnetic... 40. 6 33.7 9. 8 3. 3 54. 2 73. 0 49. 8 100/200 Separation summary:

70.9% F9103 removed. 61.7% A1203 recovered. 2.7% P93051111 concentrate.

73.0, F6203 removed. 50 0" A1103 recovered. 3.8 in concentrate.

EXAMPLE D As fines are difficult to process in beneficiation treat- A composite sample of diaspore ore was magnetically separated and comparable samples of the diaspore ore were calcined under varying conditions and magnetically separated using an induced roll high-intensity magnetic separator. The results of these tests are set forth in Table 111.

ments of ores, and are normally considered to be a waste or lost product, calcination and/or roasting of the raw ore provides an economical means of substantially reducing the fines prior to further beneficiation.

The foregoing disclosure and description of the invention is illustrative and explanatory thereof and vari- TABLE 111. PARAMETERS OF DIASPORE CLAY FOR MAGNETIC SEPARATION Separation Percent calcination conditions conditions Sample 11- O; in A110; rc- F0103 re- Time Temp. Field 0. product covered moved (lir.) C.) Atmos. (gauss) Mesh 1. 3. 4 82. O 60. 7 Non-calcined 12,000 30/400 2 11.5 82. 4 62. 3 5 00 All. 8, 030 "/400 3. 2. 3 68. 9 72. 6 20 1, 340 Air. 8, 000 30/400 4 3. 7 65. 5 58. 4 2 1, 300 Air 6, 400 ICC/200 5. .5. 7 .51. 3 78. 1 16 1,300 All. 8, 000 110/400 :7Percent 1 0103111 product was calculated on a calcined basis. 14

2 Static Loss on ignition was about ous changes may be made within the scope of the appended claims without departing from the spirit of the invention.

What is claimed is:

1. A method of improving the grindability or grinding characteristics of aluminus clays or alumina-silica ores containing iron species, wherein the clays or ores are 1 3. The method of claim 1, wherein the oxidative medium is preheated to a temperature of at least about 1000 C.

4. The method of claim 1, wherein the alumina-silica ore is a diaspore clay, kyanite clay or k yanite concentrate.

5. The method of claim 1, wherein the aluminus clay contains diaspore, boehmite and kaolinite as the predominant minerals and siderite, goethite, and he matite in substantially lesser amounts.

6. The method of claim 1, wherein the alumina-silica ore is pre-crushed or ground to a particle size of about one-quarter inch to about one-half inch in diameter prior to thermal treatment.

7. The method of claim 1, wherein the alumina-silica ore is pre-processed to about 3 mesh U. S. Sieve Series prior to thermal treatment or calcining.

8. The method of claim 1, wherein the alumina-silica ore is calcined or thermally treated at a temperature of from about 1 C to about 1400 C.

9. The method of claim 1, wherein the alumina-silica ore is calcined or thermally treated for a period of at least about two hours.

10. The method of claim 1, wherein after thermal treatment, the alumina-silica ore is ground and/or crushed to a particle size of about 40 mesh U. S. Sieve\ Series or less. 

2. The method of claim 1, wherein the oxidative medium is air or oxygen.
 3. The method of claim 1, wherein the oxidative medium is preheated to a temperature of at least about 1000* C.
 4. The method of claim 1, wherein the alumina-silica ore is a diaspore clay, kyanite clay or kyanite concentrate.
 5. The method of claim 1, wherein the aluminus clay contains diaspore, boehmite and kaolinite as the predominant minerals and siderite, goethite, and hematite in substantially lesser amounts.
 6. The method of claim 1, wherein the alumina-silica ore is pre-crushed or ground to a particle size of about one-quarter inch to about one-half inch in diameter prior to thermal treatment.
 7. The method of claim 1, wherein the alumina-silica ore is pre-processed to about 3 mesh U. S. Sieve Series prior to thermal treatment or calcining.
 8. The method of claim 1, wherein the alumina-silica ore is calcined or thermally treated at a Temperature of from about 1100* C to about 1400* C.
 9. The method of claim 1, wherein the alumina-silica ore is calcined or thermally treated for a period of at least about two hours.
 10. The method of claim 1, wherein after thermal treatment, the alumina-silica ore is ground and/or crushed to a particle size of about 40 mesh U. S. Sieve Series or less. 